Recently, with technical evolution of a mobile phone and a smart phone, services and applications using position information of a user have been provided one after another. Accordingly, there is an increasing need for a GNSS receiver that can acquire accurate position information and that operates with low power consumption. Here, the GNSS receiver is a receiver that has functions of receiving a wireless signal (positioning signal) using 1.5 GHz band transmitted from a low earth orbit satellite (positioning satellite), and calculating a position of the receiver and time.
Although a global positioning system (GPS) of which the United States takes the lead is well known, services such as a global navigation satellite system (GLONASS) developed in Russia, a BeiDou developed in China, and a Galileo mainly developed in the European Union (EU) are also being started. Accordingly, the realization of the GNSS receiver capable of demodulating positioning signals from a plurality of these positioning satellites is expected (for example, see Patent Document 1).
FIG. 1 shows an exemplary structure of a conventional GNSS receiver. As shown in FIG. 1, in the conventional receiver, an intermediate frequency (IF) signal has been acquired by frequency conversion of a reception signal into intermediate frequency using a different mixer for each of the positioning satellites such as a GPS satellite and a GLONASS satellite. Thereafter, the acquired IF signal has been supplied to an analog/digital (A/D) converter using a path different in each IF signal and then, transmitted to a demodulating unit in the next stage.
Specifically, in a GPS processing unit, the reception signal from the GPS satellite is input to a mixer (MIX1) via a low noise amplifier (LNA), mixed with a local oscillation signal FLO1 from a PLL circuit, and converted into the IF signal of about 4 MHz. Thereafter, the IF signal is transmitted to the A/D converter via a low pass filter (LPF) and an amplifier (AGCAMP).
On the other hand, in a GLONASS processing unit, the reception signal from the GLONASS satellite is input to a mixer (MIX1) via a low noise amplifier (LNA). Then, after the reception signal is mixed with the local oscillation signal FLO1 from the PLL circuit, and the frequency conversion is performed therein, the reception signal is input to a mixer (MIX2) via a low pass filter (LPF) and an amplifier (AGCAMP). After the mixer (MIX2) mixes the reception signal with a local oscillation signal FLO2 from the PLL circuit and performs the frequency conversion, the reception signal is transmitted to the A/D converter via a low pass filter (LPF).
In the phase locked loop (PLL) circuit, the local oscillation signal FLO1 generated from one oscillator (LO1) is input to the mixer (MIX1), the local oscillation signal FLO2 divided by a divider is input to the mixer (MIX2) and furthermore, a clock signal for A/D conversion divided by the divider is input to the A/D converter.
In summary, in the conventional GNSS receiver, a reception process for the reception signal has been performed by providing a different circuit (for example, the GPS processing unit and the GLONASS processing unit) for each of satellite positioning systems such as the GPS and the GLONASS. As a result, as shown in A in FIG. 2, a reception frequency band is adjusted by the GPS processing unit so as to be capable of receiving a signal band of the reception signal from the GPS satellite. In addition, as shown in B in FIG. 2 and C in FIG. 2, a reception frequency band is adjusted by the GLONASS processing unit so as to be capable of receiving a signal band of the reception signal from the GLONASS satellite.